The fundamental objective of this research is a quantitative understanding of the stability of the DNA-histone core interaction in the nucleosome. This will be analyzed by studies of (a) the kinetics of nucleosome sliding on DNA, and (b) the dissociation equilibria of nucleosomes. Dissociation equilibria will be interpreted in terms of a model which includes the dissociation of the histone octamer into hexamers, tetramers and dimers of the histones. Sedimentation equilibrium will be used to analyze the histone core dissociation, and a combination of sedimentation equilibrium, sedimentation velocity and gel electrophoresis will be employed for the nucleosome dissociation studies. The effects of histone acetylation will be assayed, using reconstituted particles enriched in modified histones. The sliding process will be analyzed in two ways. Direct measurement of sliding of a histone core reconstituted in a phased fashion on a cloned DNA fragment will be used to determine the fundamental mechanism and basic sliding rate. The kinetics of nucleosome dissociation (which seems to involve a sliding mechanism) will be studied using circular dichroism and/or a new electrophoretic technique. Again, the influence of histone modification on the rate will be studied. There is evidence that stability of nucleosomes and their displacement on DNA may be of major importance in such processes as DNA replication, repair and transcription. Therefore, a quantitative analysis of DNA-histone interactions may be vital to a full comprehension of these processes on eukaryots.